From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: [PATCH RT 3.18] ring-buffer: Mark irq_work as HARD_IRQ to prevent deadlocks Date: Thu, 16 Apr 2015 16:06:54 +0200 Message-ID: <552FC1FE.4020406@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Cc: Linux Kernel Mailing List , Steven Rostedt To: Sebastian Andrzej Siewior , RT Return-path: Received: from goliath.siemens.de ([192.35.17.28]:59675 "EHLO goliath.siemens.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754219AbbDPOTp (ORCPT ); Thu, 16 Apr 2015 10:19:45 -0400 Sender: linux-rt-users-owner@vger.kernel.org List-ID: ftrace may trigger rb_wakeups while holding pi_lock which will also be requested via trace_...->...->ring_buffer_unlock_commit->...-> irq_work_queue->raise_softirq->try_to_wake_up. This quickly causes deadlocks when trying to use ftrace under -rt. Resolve this by marking the ring buffer's irq_work as HARD_IRQ. Signed-off-by: Jan Kiszka --- I'm not yet sure if this doesn't push work into hard-irq context that is better not done there on -rt. I'm also not sure if there aren't more such cases, given that -rt turns the default irq_work wakeup policy around. But maybe we are lucky. kernel/trace/ring_buffer.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index f4fbbfc..6a1939e 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1252,6 +1252,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu) init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); init_waitqueue_head(&cpu_buffer->irq_work.waiters); init_waitqueue_head(&cpu_buffer->irq_work.full_waiters); + cpu_buffer->irq_work.work.flags = IRQ_WORK_HARD_IRQ; bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), GFP_KERNEL, cpu_to_node(cpu));